Foundry sand binder and process of preparation



FOUNDRY-:SANDTBENDER AN D :IROCESS rOF PREPARATION Harold K. Sa'lzberg, Bainbridge, Y., assignor t o The Borden Company, "New York, N. Y., a corporation of New Jersey No Drawing. rApplicationllanuaryifi, 1956, Serial No. 558,821

3 Claims. (Cl. 26017.2)

This invention relates to a binder composition for foundry sand. The invention is particularly useful in b'onding sand cores, and for that reason will 'be illustrated by description inconn'e'ction with such use.

Foundry-cores are customarily :formed #of sand and a binderincluding-ordinarilystarch or th'e like and a core oil. The-binder-holds the sand 'together' during-the forming and drying of the :cores. in the :ultimate use of the cores, to provide hollow spaces in castings made by pourin'g hot, molten'm'etal around the cores, the binder is burnedout. 'Thecores are-thus reduced moreor less to free flowingsand that falls away from the s'dli'dified casting.

Forbest=results, thebinder composition =shoul'd minimize the tendency of the dried core, even when bonded with a waterabsorptive adhesive, to softenonexposure to atmospherichumidity or to the humidityof a green sand mold. In additionflthe binder composition should provide adequate green strength of the 'eore so that -it may :be handled safely up totth'e drying s'tagepgive suificient strength to-the coreg after drying, to:cause-the'-core to withstandhandling and also pressure of metal against the core without breaking :or premature :collapse; and give 1a minimum of gas :pressure in contact with the hot metal :being :cast, so .as' to decrease ithe hazard: of porosity being induced :in :the metal ieasting -ton contact with the core. .Also, the timere'quiredfonbakingthe fc'ore should be brief.

This invention provides a binder composition for foundry covers that is an improvement over binders heretofore used in meeting this combination ofrequirements.

Briefly stated, the invention comprises a foundry sand binder composition including an aqueous dispersion 'of water absorptiveadhesive, a resin, and a wax, the wax being dispersed in wateras the continuousphase and the water suitably containing 'an emulsifying agent for the wax. The'invention comprises also sand bonded with Ithecompositionand theherein describedprocess o'fbonding the sand.

Use of wax has been described as a lubricant .o'ft-sand grains. Lubricating is the opposite of bonding. 'Yet I "find the waxactualy more effective, when used jointly with starchy adhesives, in imparting green strength .to sand cores than are such adhesives themselves.

.There is made an aqueous dispersion of relativelylow melting wax, such as petroleum wax, disperse'dfitself in water or 'in an aqueous solution. The dispersion of the wax so made is mixed intosand, .with astarch adhesive, .a resinous formaldehyde .condensation product, and water in amount tomoistenthe :sandandcauseadherence when the moistened sand is molded into the shape of a core. The core is then dried.

In use the core is suitably disposed in=a;mold and molten steel orlike metal is poured around the-core and allowed to cool and solidify, so astoform ahollow space of desired shape, size, and location within 'the casting 'thus produced. The pressure of gas developed from the binder composition, as the latter 'burns 'outat the ignition Patent 0 2,8 13,840 Patented Nov. 1-9, 19.57

.2 temperature reached-.duringthe casting, vis considerable. Preformed gas escape vents :are sometimes necessary in 'the foundry core, therefore, in order tominimizepassage .of ,gas .into the cast metal as the gas escapes from the regionof l its formation.

Since water is the continuous phase in the wax emulsion, the wax is 'prevented from 'forminga waterrepellent coatingor layer over the sand before the aqueous dispersion of starch or similar adhesive makes contact with the grains of the sand. The water absorptiveness of the adhesive, on the other hand, brings the wax in .the aqueous emulsion into such association with .thevadhesive that, in the dried core, the 'vwaxhdecrea-ses the water tabsorptiveness of r the \adhesive.

The wax, at the temperature of drying and higher temperaturesto whichthe cores-are exposed, :volatilizes in ,parts. The volatilized part escapesas heavy-molecules of relatively low volume in proportion to the mass, in distinction from the large specificwolumes .of the ;perma- .nent .gases developed by the ieombustion -.of \conventional adhesives of the type of starch. Also the-.use-oftthe wax decreases .the proportion of theisaid adhesive required.

As to materials used, the sand may be any good foundry sand, a number of commercial grades of which are shown in the examples later herein.

The adhesive is one that 'is combustible. It is water absorptive, that is, swells, or finally dissolves in water and suitably both. Examples of adhesivesthat'meetthe requirements and illustrate the class of materialsto be used are the polymeric carbohydrates such as starchy materials, particularly pregelatinized "corn starch, and cereal and tuber-products of high'starch content, as"for instanceycorn, rice or-potato fiouror starches'there'from.

supplementary 'binders are used-'toadvantagewith the water absorptive adhesive. Examples are resins such as water dispersible condensation products of formaldehyde with urea, phenol, or the like.

The wax used is one that vaporizes or smokes tat the temperature of use of the core. Petroleum waxes give a special effect. In contact with .the hot metal being cast, as in either liquid or vapor form at 1000" F. or higher, they are decomposed by the heat, with deposition of carbonon the surface of the core. They improve the smoothness of the metal cast .thereagainst. Examplesof waxes that are suitable and that may be used are the tvarious grades of petroleum wax including such usual paraifin waxes as refined, slack, sweat,-.scale, block,-para-, and microcrystalline wax.

The wax, as introduced into the bindercomposition, may be emulsified in water by any conventional emulsid oleates and stearates.

fatty acid soaps such as alkali metal oleates andstearates, ethanolamine oleates and stearates, and alkyl amine The separation method of prep aring the emulsion may be conventiently used. .In this method the fatty acid is dissolved in the paratfin andthe alkali in the water, the molten mixture thenlbeing poured into the alkaline solution under agitation. Protective colloids, such as alkaline caseinates, may also be incorporated to provide good stability to the emulsion. The whole formula (wax, water, and emulsifying agent) may be passed through a colloid millaor other "fine-dispersal mill to attain smal11particle size-ofthe dispersed phase. Emulsions of average particle sizein the 'rangeof 0.22. '0 microns are readily attained and' are satisfactory for the pra-ctice of this invention.

The ratio of wax to waterin the :final .produ'cti-rmay vary in a widerange. However, the emul-sionzis most conveniently made and handledinconcentrationswithin. the range .of .20%40% of-emulsified .on-the'weight; of wax and water.

As to proportions, I may use somewhat less than the customary amounts of the water absorptive adhesive or of the combination thereof with the supplementary adhesives such as urea-formaldehyde resin. The wax provides a sparing action on the other materials needed. Suitable 5 proportions of the whole binder composition are l-l parts for 100 of the sand, all being on the dry basis and all proportions being expressed here and elsewhere herein as parts by weight unless specifically stated to the con- When cores are made with such binder combinations, heated to dryness and partially cured, the core binder does not swell, crumble, or soften appreciably on exposure to water or humidity under the conditions of use of the cores.

Example 1 The example shows the effect of inclusion of the wax emulsion on the green compression and also the dry tensile strength of the cores.

The following test data are for cores made and tested in comparable manner, except that cores #1 were made with a binder composition including no wax emulsion, for contrast with cores #2 and #3 containing different proportions of the said emulsion according to the present invention.

CORES MADE WITHOUT AND WITH WAX Proportions Cor #1 #2 #3 Materials:

Foundry sand, N. I. #80 2.000 2, 000 2,000 Foundry sand MeOonnelsville #180 2, 000 2, 000 2, 000 Corn flour, Mogul (adhesive) 40 20 20 Water (added with corn flour) 180 177 174 Boric acid (accelerator) 10 i0 10 Urea-formaldehyde cond. product 40 40 40 Stearic acid (parting agent) 5 O 0 Kerosene (to disperse parting agen 16 0 0 Paraifin wax emulsion (25% wax) 0 4 3 Gas forming ingredients in the core, percent" 2. 12 1. 60 1. 70

Results:

Stickiness in mulling operation None Very Very slight slight 35 42 41 1. 3 1. 6 l. 6

107 168 188 123 158 158 60 min. at 375F 83 167 154 The urea-formaldehyde product in the compositions tabulated above was made with 1 mole of urea to 1.8 moles formaldehyde and condensed with alkaline catalyst to the water soluble, A-stage resin.

When paraffin wax emulsion replaced the combination of parting agent and kerosene, the amount of corn flour could be reduced without sacrifice of green or baked core strength. In fact these strength values are higher when the wax emulsion isused. Also this formula change reduced the gas forming ingredients by 25% in cores No. 2 and by 20% in core No. 3.

Example 2 The procedure of Example 1, preparations No. 2 or No. 3 is followed except that there are introduced parts of phenol-formaldehyde resin made by condensing 1 mole of phenol with 2 moles of formaldehyde to watersoluble resinous condition by usual technique. Other proportions of phenol to formaldehyde may be used to give the water-soluble product.

Also, the kerosene and the parting agent are omitted when the resin is the phenol-aldehyde product.

Example 3 A core sand mix was prepared on the following formula:

Component: Parts Foundry sand, N. I. No. 80 100 Corn flour, Mogul (adhesive) 0.5 Water (added with corn flour) 4 Urea-formaldehyde cond. product 1 Paraflin wax emulsion (25% Wax) 0.3

The wet core sand mix was taken to an aluminum foundry where two 8 lb. cores were made in a wood core box designed for a casting to be machined and used as a housing for a hydraulic lift truck. The cores were baked for 2 hours at 350 F., one-half of the regular time for these cores made in oil sand. My cores, without being coated, were set in a green sand mold in the usual manner. Aluminum alloy 417 was poured at 1350 F. without any changes in the conventional procedure. The casting was knocked out after 30 minutes, allowed to cool and inspected. The cored surface was completely smooth and free of any roughness, whereas the general run of these castings as ordinarily made showed, upon inspection, areas of sand roughness. The smoother surface of my casting is attributable in part to the evolution of less gas from the core, thereby minimizing disturbance of the core surface as the molten metal contacts it.

The casting was also found to be sound and to pass inspection on every point.

Example 4 The procedure of Example 3 is followed except that the corn flour there used as the starchy adhesive is replaced by an equal weight of any other flour or starch disclosed herein.

It will be understood that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purpose of illustration which do not constitute departures from the spirit and scope of the invention.

What I claim is:

l. A foundry sand binder composition comprising 0.25-5 parts by weight of starch, water, 0.0l0.1 part of paraffin wax and 025-5 parts of resin, the resin being selected from the group consisting of water soluble urea formaldehyde condensation product and water soluble phenol formaldehyde condensation product, the paraflin wax being vaporizable in part at the temperature of casting of metal against foundry sand and being heat decomposable to give carbon at a temperature of 1,000 E, the wax being dispersed in emulsified form and as the discontinuous phase in the water, and the whole being in emulsified condition.

2. In binding foundry sand, the process which comprises mixing parts by weight of the sand with the binder composition of claim 1 in proportion to provide 0.25-5 parts of starch on the dry basis and heating the resulting mixture to a temperature above the boiling point of water, continuing said heating until the water of the said composition is substantially completely evaporated, and then raising the temperature of the dried mixture to that of formation of vapors of the parafiin wax and to the temperature of heat decomposition of said wax with formation of a carbon deposit over the surface of the sand.

3. The composition of claim 1, the said starch being in pregelatinized condition.

References Cited in the file of this patent UNITED STATES PATENTS 2,600,321 Pyle June 10, 1952 2,684,344 Phillips July 20, 1954 OTHER REFERENCES British Plastics, December 1952, volume 25, pages 410415. 

1. A FOUNDRY SAND BINDER COMPOSITION COMPRISING 0.25-5 PARTS BY WEIGHT OF STARCH, WATER,0.01-0.1 PART OF PARAFFIN WAX AND 0.25-5 PARTS OF RESIN, THE RESIN BEING SELECTED FROM THE GROUP CONSISTING OF WATER SOLUBLE UREA FORMALDEHYDE CONDENSATION PRODUCT AND WATER SOLUBLE PHENOL FORMALDEHYDE CONDENSATION PRODUCT, THE PARAFFIN WAX BEING VAPORIZABLE IN PART AT THE TEMPERATURE OF CASTING OF METAL AGAINST FOUNDRY SAND AND BEING HEAT DECOMPOSABLE TO GIVE CARBON AT A TEMPERATURE OF 1,000*F., THE WAX BEING DISPERSED IN EMULSIFIED FORM AND AS THE DISCON-TINUOUS PHASE IN THE WATER, AND THE WHOLE BEING IN EMULSIFIED CONDITION. 